Whey vs Casein at Rest

As discussed previously, whey, casein, and soy all have differing amino acid compositions and, seemingly more important, differing postprandial kinetics. The speed of amino acid absorption has a major impact on postprandial PS and PB responses of a meal. Whey protein is a very fast absorbed protein and, after ingestion, the appearance of circulating amino acids is rapid, increased, and transient. Whey protein has been shown to quickly and transiently increase whole-body PS as well as amino acid oxidation. Boirie et al. found that the increase in protein synthesis was 68% above baseline during the period from approximately 40 min to just after 140 min after ingesting a whey drink.9 Casein is a slowly absorbed protein, and the appearance of postprandial circulating amino acids is slow, low, and prolonged. Casein tends to inhibit PB when consumed at rest and has a slight, but relatively long, increase in PS. The pattern of amino acid delivery with casein appears to lead to better leucine balance (net protein state) than whey at rest. It is interesting to note that casein ingestion does not lead to large increases in circulating levels of amino acids as was observed in many early amino acid infusion studies or whey ingestion studies. To further support these points, a study conducted by Dangin et al.22 compared casein to a supplement containing amino acids in the same amount as native casein, and compared whey protein to that same dose of whey spread out over 13 small feedings every 20 min. All the feedings were composed of 30 g of protein. The two meals (casein and whey feedings every 20 min), which were designed to mimic casein, showed results that were similar to the previously listed results. The single whey feeding and casein amino acids group mimicked the previous results of whey protein.22 It is of interest to note that the frequent whey feeding increased net leucine balance to 87 ^mol/kg-1 and the casein feeding increased leucine balance to 38 ^mol/kg-1.22 These authors did not statistically compare these values. Overall, it would appear that casein protein, and its slow absorption rate, leads to a greater positive net whole-body protein state than single feedings of whey protein or amino acids at rest. Additionally, frequent small feedings of whey proteins may lead to the greatest net leucine balance, indicative of the greatest protein accretion.

Your Heart and Nutrition

Your Heart and Nutrition

Prevention is better than a cure. Learn how to cherish your heart by taking the necessary means to keep it pumping healthily and steadily through your life.

Get My Free Ebook


Post a comment